This invention relates to the fabrication of semiconductor devices and, more particularly, to a diffusion furnace adjunct useful in the fabrication of semiconductor devices.
In a recent U.S. Pat. No. 4,256,052, entitled "TEMPERATURE GRADIENT MEANS IN A REACTOR TUBE OF VAPOR DEPOSITION APPARATUS," which issued on Mar. 17, 1981 to R. V. Johnson, et al. and assigned to the same assignee as the subject application, a diffusion furnace is described wherein the furnace tube has an elongated portion that is provided with layers of thermal insulation. The presence of the insulated portion serves to minimize the thermal shock to a semiconductor substrate during periods when the substrate is either introduced into or when it is removed from the heated furnace. Accordingly, to be most effective, the substrates are inserted slowly at the outset of processing so that the wafers will not suddenly be exposed to an elevated temperature. Conversely, the processed substrates are removed slowly at the conclusion of the processing in order to minimize the thermal shock of leaving the heated ambient for the relative cool temperature associated with the processing room.
In order to facilitate the explanation of the operation of our device, the conventional structure of the prior art as shown in U.S. Pat. No. 4,256,052, is hereby incorporated in its entirety into the subject application.
While this prior art furnace tube extension serves a valuable purpose, it has been found that the necessary slow insertion and removal lengthens the processing time and thus reduces the throughput of a system. Further, since the furnace tube is operated under a slightly positive pressure, the heated reactants, upon exiting the furnace tube tend to dissipate heat into the controlled environment of the room.
Thus, since the desiderata are small increases or decreases in temperature per unit length it is reasoned that considerable processing time can be saved by a controlled cooling and heating of a reception chamber in which the substrates are maintained.